The Weeping Angels apparently originated with Steven Moffat seeing a statue of a weeping angel in a structure in a cemetery and returning later to find out it was gone. At least according to this RadioTimes article. They first appeared in 2007 in the episode Blink.

I am wondering if this mechanic has been done before though?

It’s become quite common in the indie horror scene.

In the 2007 video game Sherlock Holmes: Nemesis Watson would not move if in the player’s view but would teleport behind the protagonist when given the opportunity. A video of it can be found here.

Considering this could be an easy place holder for developers or a way to get around programming walking animations all together I’m surprised no one took the idea and ran with it before then.

All that said it could have been used in books or movies. Maybe a twist on some other vision-centric myth like Medusa or Orpheus and Eurydice?